The present invention relates to an ATM switching unit, and more specifically, to an ATM switching unit for accommodating a duplicated ATM cell transfer line.
In an ATM (Asynchronous Transfer Mode) network, ATM switching unit (ATM switching units) are provided as nodes (switching points) for constituting the ATM network. The ATM switching unit connects a plurality of lines for constituting the ATM network (a plurality of reception lines and a plurality of transmission lines). Then, when a cell transmitted from another transfer apparatus (another ATM switching unit, etc.) is received from the reception line, the ATM switching unit transmits the cell from the transmission line functioning as an output path by using transfer path information stored in a header of this received cell.
As transfer path information of a cell, a VPI (virtual path identifier)/VCI (virtual channel identifier) are stored in a header of a cell. The ATM switching unit contains a line processing unit for converting a VPI/VCI into address information about a counter party (transfer destination), and an ATM switch for switching a cell to any one of plural transfer lines based on this address information. Then, when the line processing unit and the switch are actuated, a plurality of cells which are received by the same ATM switching unit and contain the same VPIs/VCIs are transmitted from the same transfer line in this same ATM switching unit.
By the way, a memory capacity employed in the ATM switching unit is limited. For this reason, in the line processing unit and the switch, the above-explained address converting process and routing process cannot be carried out while directly using a VPI (12 bits) and a VCI (16 bits) of a received cell. Therefore, the line processing unit converts the VPI/VCI of the received cell into 13-bit reduced information (path identifier) called as an ICID-A, and executes the above-explained address converting process and routing process with employment of this ICID-A.
Also, there are duplicated lines connected in the ATM switching unit in view of important factors of transferred data. In other words, lines connected in the ATM switching unit are constructed of a working line for a presently operable system and a protection line for a spare operation system, and cell transmission is carried out by employing this working line under normal condition, whereas when a failure happens to occur in this working line, this troubled working line is switched to the protection line so as to perform the cell transmission.
FIG. 12 is a functional block diagram for showing an arrangement of a line processing unit (input line processing unit) 1 containing a duplicated line in a conventional ATM switching unit. In this drawing, the line processing unit 1 is arranged by an individual unit, a VCC table (common unit) 3, and an address converting unit 4 provided in the VCC table 3. The individual unit is constituted by a reducing unit ACT (action) connected to a working line WL, and a reducing unit SBY (standby) connected to a protection line PL. The VCC table (common unit) 3 is connected to the reducing unit ACT and the reducing unit SBY, respectively. Then, the VCC table 3 of the line processing unit 1 is connected to a switch 5.
Both the working line WL and the protection line PL transfer the same cell, and the same cell is entered via either the working line WL or the protection line PL to the reducing unit ACT and the reducing unit SBY. When a cell is inputted, both the reducing unit ACT and the reducing unit SBY convert a VPI/VCI stored in a header of this inputted cell into an ICID-A, and thereafter transmit the cell toward the VCC table 3.
In this case, the cell entered into the reducing unit SBY corresponds to a spare cell, and therefore is not required unless a failure happens to occur in the working line WL. As a result, the cell sent out from the reducing unit SBY is forcibly discarded before being entered into the VCC table 3 under such an initial condition that no failure happens to occur in the working line WL. Accordingly, only the cell sent out from the reducing unit ACT is inputted into the VCC table 3. As a result, the following problem can be avoided. That is, the spare cell will flow into the ATM switching unit, and thus may give the unnecessary processing workload to this ATM sustaining apparatus.
On the other hand, the cell sent out from the reducing unit ACT is entered into the address converting unit 4 of the VCC table. Upon receipt of the cell sent out from the reducing unit ACT, the address converting unit 4 converts the ICID-A saved in the header of this cell into address information about a counter party, and then transfers the cell to the switch 5. Then, when the switch 5 receives the cell from the VCC table 3, this switch 5 performs the switching operation in accordance with the address information stored in the header of this cell.
However, the above-described line processing unit 1 of the conventional ATM switching unit owns the following problems. That is, the presently available ATM switching unit is capable of connecting, for instance, 16 sets of lines at maximum, and is provided with the reducing units, the total number of which is selected in accordance with a total number of lines to be connected in order to house the respective lines. The respective reducing units are connected to the VCC table 3. To simplify the structure of the presently available ATM switching unit, the duplicated line are set as follows: Only when the reducing unit SBY for connecting the protection line PL is installed adjacent to the reducing unit ACT for connecting the working line WL, the cell transferred to the protection line PL is forcibly discarded. In other words, the discarding process of the cell transferred to the spare cell line is carried out based upon the connecting position of the duplicated lines.
For that reason, in such a case that the protection line PL is connected in such a reducing unit located apart from namely not located adjacent to the reducing unit for connecting the working line WL, the cell transferred via the protection line PL is not discarded before being entered into the VCC table 3, but would flow into the ATM switching unit.
As a consequence, in the case that a user who presently uses a single cell line wants to duplicate the cell lines in the conventional ATM switching unit, such a reducing unit must be empty which is located adjacent to the reducing unit into which this single cell line has been connected. Also, when duplicated lines are newly set in the conventional ATM switching unit, two sets of reducing units located adjacent to each other should be empty.
In view of the above-mentioned problems, the present invention has been made, and therefore, it is an object of the present invention to provide an ATM switching unit capable of discarding a cell transferred to a spare cell line irrespective of connecting positions of duplicated lines, and thus capable of more properly duplicating lines.
To solve the above-described problems, an ATM switching unit of the present invention may employ the following arrangements:
That is, an ATM switching unit according to a first aspect of the present invention is comprised of: cell receiving means for receiving the same cells from two lines through which the same cells are transferred; cell information storing means for storing specific information indicative of a cell of a presently operable system into only the cell received from one line among the cells received by the cell receiving means, and for storing the specific information into only the cell received from the other line when a failure happens to occur in the one line; discarding means for receiving the cells from the cell information storing means to discard such a cell into which the specific information is not stored; and transferring means for specifying an output path of such a cell which is not discarded by the discarding means, and for transferring the cell to the output path.
In accordance with the first aspect of the present invention, when the failure does not occur in one line, the cell information storing means stores the specific information into only the cell received from one line, whereas when the failure happens to occur in one line, the cell information storing means stores the specific information into only the cell received from the other line, among the cells inputted into the cell receiving unit. Thereafter, the cell is entered into the discarding means. The cell discarding means discards such a cell into which the specific information is not stored as the cell of the spare operation system. Thereafter, the transmission ring means transfers such a cell which is not discarded by the discarding means, namely the cell of the presently operable system to the output path thereof.
An ATM switching unit according to a second aspect of the present invention is comprised of: cell receiving means for receiving the same cells from two lines through which the same cells are transferred; cell information storing means for storing specific information indicative of a cell of a presently operable system into only the cell received from one line, among the cells received by the cell receiving means; and for storing the specific information into only the cell received from the other line when a failure happens to occur in the one line; discarding means for receiving the cells from the cell information storing means to discard such a cell into which the specific information has been stored; and transferring means for specifying an output path of such a cell which is not discarded by the discarding means, and for transferring the cell to the output path.
In accordance with the first aspect and the second aspect of the present invention, the cell discarding means discards the cell of the spare operation system based on the specific information stored in the cell. In other words, the cell discarding process based on the connecting position of the duplicated line is not carried out. For that reason, the cell of the spare operation system can be discarded irrespective of the connecting position of the duplicated lines. Accordingly, since the process operation by the ATM switching unit for the cell of the spare operation system can be avoided, it is possible to prevent the unnecessary processing workload from being given to the ATM switching unit.
An ATM switching unit according to the first and second aspects of the present invention is preferably arranged by that in the case that there are plural output paths of the cell which is not discarded by the discarding means, the transferring means copies the cell to produce a plurality of copied cells, a total number of which is determined in correspondence with a total number of the plural output paths, and transfers the plural copied cells to the plural output paths. With this, when the lines on the downstream side of the cell are duplicated, the cell can be sent to the respective lines. Also, the cell may be multi-cast.
Also, an ATM switching unit according to a third aspect of the present invention is comprised of: a first reception line connecting unit for connecting a reception line of a presently operable system; a second reception line connecting unit for connecting a reception line of a spare operation system, through which a cell identical to a cell transferred through the reception line of the presently operable system is transferred; a transfer line connecting unit for connecting a transfer line through which the cell is transmitted, the cell being inputted into any one of the first reception line connecting unit and the second reception line connecting unit; detecting means for detecting a failure occurred in the reception line of the presently operable system; cell information storing means for storing cell specific information indicative of the cell of the presently operable system into the cell inputted into the first line connecting unit, and for storing the cell specification information into the cell entered into the second reception line connecting unit instead of the cell entered into the first reception line connecting unit when the failure occurred in the reception line of the presently operable system is detected by the detecting means; cell discarding means for receiving the cells from the first reception line connecting unit and the second reception line connecting unit to discard such a cell into which the cell specific information is not stored; and cell transferring means for transferring the cell of the presently operable system to the transfer line connecting unit based on transfer destination address information of the cell, which has been stored in a header of the cell of the presently operable system, being equal to the cell not discarded by the cell discarding means.
The ATM switching unit according to the third aspect of the present invention is preferably further comprised of: judging means for judging whether or not the transfer line connected in the transfer line connecting unit is equal to the transfer line of the presently operable system for constituting a duplicated line based on the transfer destination address information of the cell of the presently operable system; and second call transferring means for copying the cell of the presently operable system when the judging means judges that the transfer line connected to the transfer line connecting unit is equal to the transfer line of the presently operable system, and for transferring the duplicated cell to a second transfer line connecting unit for connecting a transfer line of a spare operation system which constitutes a pair together with the transfer line of the presently operable system. With this arrangement, the cells having the same contents can be transmitted to the transfer line of the presently operable system, and also to the transfer line of the spare operation system on the transmission side of the ATM switching unit.
Also, the ATM switching unit according to the third aspect of the present invention is preferably further comprised by that: in the ATM switching unit, there are provided a plurality of the transfer line connecting units; and the ATM switching unit is further comprised of: judging means for judging whether or not the cell of the presently operable system should be transmitted to at least two transfer lines among the plurality of transfer lines connected to the plurality of transfer line connecting units based upon the transfer destination address information of the cell of the presently operable system; when the judging means judges that the cell of the presently operable system should be transmitted to at least two transfer lines, specifying means for specifying a transfer line connecting unit for connecting at least two transfer lines; copying means for copying the cell of the presently operable system in correspondence with the number of transfer line connecting units specified by the specifying means; and cell transferring means for transferring both the cell of the presently operable system and the cell copied by the copying means to the transfer line connecting unit specified by the specifying means.
Also, the ATM switching unit according to the third aspect of the present invention is preferably further comprised of: first header converting means for converting both a virtual path identifier and a virtual channel identifier into first reduced information, the virtual path identifier and the virtual channel identifier being stored in the headers of the cells inputted into the first reception line connecting unit and the second reception line connecting unit; second header converting means for converting the first reduced information stored in the header of the cell of the presently operable system into second reduced information produced by reducing the first reduced information and the output path information of the cell of the presently operable system; and third header converting means for converting the second reduced information stored in the header of the cell of the presently operable system into the transfer destination address information of the cell of the presently operable system.
With employment of the above-described arrangements, both the virtual path identifier and the virtual channel identifier are converted into the first reduced information, so that the memory capacity employed in the ATM switching unit can be reduced. Also, the first reduced information and the output path information, which are required to acquire the transfer destination address information of the cell, are reduced to the second reduced information. As a result, the memory capacity required to process the cells can be suppressed.
In accordance with the ATM switching unit of the present invention, the cell of the spare operation system can be discarded irrespective of the connecting positions of the duplicated lines. As a consequence, the lines can be duplicated with higher flexibility than that of the conventional ATM switching unit.